Planetary gear train for automatic transmission

ABSTRACT

In an automatic transmission incorporating a planetary gear transmission at a rear stage of a four-element torque converter comprising two stators, a turbine and a pump; a planetary gear train of an automatic transmission, wherein a reversal torque of a first stator reversing in a low speed ratio zone is converted into a normal torque by the planetary gear train so that this output from the first stator can be added to an output shaft, when a first speed of the planetary gear transmission is selected; a friction element is provided for limiting a rotation of the first stator in the speed ratio zone where the first stator rotates in the reverse direction, a one-way clutch for transmitting a torque only in a specified direction is installed, and the first stator is permitted to run idle by this one-way clutch so that a fluid loss in a stator portion can be minimized, when a second speed of the planetary gear transmission is selected.

BACKGROUND OF THE INVENTION (Industrial Useful Field)

This invention relates to an improvement in a planetary gear train whichconstitutes, for example, an automatic transmission for automobile incombination with a four-element torque converter.

(Prior Art and its Problem)

A conventional Simpson's planetary gear train of this type isconstructed as illustrated in FIG. 2.

The planetary gear, in FIG. 2, includes a pair of planetary gearassemblies 10 & 12 comprising planetary gears, planetary carriers, sungears and ring gears disposed at a rear stage of a three-element torqueconverter consisting of a stator, a turbine and a pump; two sun gears 14& 16 connected together; a planetary carrier 18 connected to ring gear20; and an output from planetary carrier 18.

Brakes B1 & B2 and clutches C1 & C2 for controlling such gears arearranged in such Simpson gear train and the brakes together with theclutches work as "0" in the following Table 1 to carry out a speedchange of three forward speeds and one reverse speed.

                  TABLE 1                                                         ______________________________________                                        (Prior Art)                                                                             Brake & clutch                                                                C1  C2          B1    B2                                            ______________________________________                                        1st         --    0           --  0                                           2nd         --    0           0   --                                          3rd         0     0           --  --                                          Rev         0     --          --  0                                           ______________________________________                                    

A stage number of speed change has recently been multiplied from threeforward speeds to four forward speeds in order to improve a performanceof tractive force.

In the foregoing Simpson's planetary gear train, however, the speedchange of three forward speeds and one reverse speed is used and a speedchange of four forward speeds and one reverse speed becomes complicatedin structure and is unsuitable for practical application.

Further, a conventional general Ravineaux planetary gear train isconstructed as illustrated in FIG. 3 and includes.

A planetary gear 110 which is comparatively long in its axial directionand meshes with a sun gear 116 and a ring gear 120 to form a single rowplanetary gear. Moreover, the planetary gear 110 is carried by aplanetary carrier 114, a planetary gear 112 is carried by the planetarycarrier 114 while meshing with the planetary gear 110, and the planetarygear 112 meshes with a sun gear 118 to form a double row planetary gear.Furthermore, a ring gear 120 meshing with an outer periphery of theplanetary gear 110 is connected to an output gear 122.

Brakes B1 & B2 and clutches C1, C2 & C3 for controlling these gears arearranged therein, and the brakes together with the clutches work, astabulated "0" in the following Table 2, to carry out a speed change offour forward speeds and one reverse speed.

For a speed change of three forward speeds, the clutch C3 is omitted.

                  TABLE 2                                                         ______________________________________                                        (Prior Art)                                                                   Brake & clutch                                                                C1             C2    C3        B1  B2                                         ______________________________________                                        1st     --         0     --      --  0                                        2nd     --         0     --      0   --                                       3rd     0          0     --      --  --                                       4th     --         --    0       0   --                                       Rev     0          --    --      --  0                                        ______________________________________                                    

A stage number of speed change has recently been multiplied from fourforward speeds to five forward speeds in order for improving performanceof tractive force.

In the conventional planetary gear train, however, the number ofclutches will increase with an increase in a stage number of speedchanges, and the structure and control become complicated.

(Object of the Invention)

An object of the invention is to improve performances of tractive forcefor a starting first speed and a next second speed to decrease one speedchange stage from the stage number of speed change in a planetary geartrain combined with a four-element torque converter, so that itsstructure and control can be simplified to provide structures ofSimpson's and Ravineaux's planetary gear train applied with the presentinvention.

(Structure of the Invention)

(1) Technical measure

In an automatic transmission incorporating a planetary gear transmissionat a rear stage of a four-element torque converter comprising twostators, a turbine and a pump; a planetary gear train for an automatictransmission, wherein a reversal torque of a first stator reversing in alow speed ratio zone is converted into a normal torque by the planetarygear train so that this output from the first stator can be added to anoutput shaft, when a first speed of the planetary gear transmission isselected; a friction element is provided for limiting the rotation ofthe first stator in the speed ratio zone where the first stator rotatesin the reverse direction; and the first stator, equipped with a one-wayclutch, transmitting a torque only in a specified direction, is adaptedto run idle so that a fluid loss at a stator portion can be minimized,when a second speed of the planetary gear transmission is selected.

(2) Function

In the first speed, the normal torque of the turbine and the reversaltorque of the first stator are combined by the planetary geartransmission for a combined high torque ratio.

In the second speed, the first stator is locked by the friction elementand at the same time the first stator is adapted to run idle in a speedratio zone before the second stator runs idle for obtaining a highefficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic structural diagram showing a first embodimentaccording to the invention.

FIG. 1a is a graphical illustration of a torque ratio and an efficiencyplotted against a speed ratio in a first speed.

FIG. 1b is the same graphical illustration in second and fourth speeds.

FIG. 1c is the same graphical illustration in a third speed.

FIG. 1d is the same graphical illustration in a reverse speed.

FIGS. 2 & 3 are schematic structural diagrams showing conventionalembodiment respectively.

FIG. 4 is a schematic structural diagram showing a second embodimentaccording to the invention.

FIG. 5 is a schematic structural diagram of a third embodiment accordingto the invention.

FIG. 6 is a schematic structural diagram of a fourth embodimentaccording to the invention.

FIG. 7 is a schematic structural diagram of a fifth embodiment accordingto the invention.

FIG. 8 is a schematic structural diagram of a sixth embodiment accordingto the invention.

FIG. 9 is a schematic structural diagram of the conventional embodiment.

FIG. 10 is a schematic structural diagram of a seventh embodimentaccording to the invention.

FIG. 11 is a schematic structural diagram of an eighth embodimentaccording to the invention.

FIG. 12 is a schematic structural diagram showing the conventionalembodiment.

FIG. 13 is a schematic structural diagram of a ninth embodimentaccording to the invention.

DETAILED DESCRIPTION OF THE INVENTION (First Embodiment)

A first embodiment forming an automatic transmission providing threeforward speeds and one reverse speed for a front drive automobile willbe described with reference to FIG. 1. In FIG. 1, a member attached withthe same symbol as FIG. 2 is a member identical with or a correspondingto that of FIG. 2.

In FIG. 1, 30 is a four-element two-stage torque converter, and thetorque converter 30 is composed of a pump 32, a turbine 34, a firststator 36 and a second stator 38 etc.

The turbine 34 is connected to a turbine shaft 40, and the first stator36 is connected through a one-way clutch 42 to a stator cylindricalshaft 44. The stator cylindrical shaft 44 is disposed concentricallywith and rotatably upon the turbine shaft 40. The one-way clutch 42 runsidle when the first stator 36 rotates in the same direction as theturbine 34 i.e. in normal direction, and locks when the first statorrotates in the opposite direction, so as to transmit a reversal torqueof the first stator 36 to the stator cylindrical shaft 44. The secondstator 38 is connected through a one-way clutch 46 to a fixedcylindrical shaft 48. The fixed cylindrical shaft 48 is disposedradially outside of and concentrically with the stator cylindrical shaft44. The fixed cylindrical shaft 48 is connected to a housing 50.Further, the turbine is equipped with a lock-up clutch 52. A so-calledSimpson's planetary gear train, which will be described later indetails, is combined with a rear stage of the above-mentioned torqueconverter 30 to constitute an automatic transmission.

The turbine shaft 40 extends in a right direction of a planetary gearassembly 10 of FIG. 1 to be connected to a ring gear 22 (number ofteeth: Zrl). The ring gear 22 meshes with a planetary gear 24 carried bya planetary carrier 18. An output gear 26 is connected to anintermediate portion of the planetary carrier 18, and a ring gear 20(number of teeth: Zr2) is fixed to a left end in FIG. 1 of the planetarycarrier 18. A brake B3 for limiting rotation of the turbine shaft 40 isprovided radially outside of the turbine shaft 40.

A planetary gear 28 of a planetary gear assembly 12 is carried by aplanetary carrier 29, and a brake B2 is equipped to the planetarycarrier 29. A clutch C1 is interposed between the turbine shaft 40 andthe stator cylindrical shaft 44 connecting to a sun gear 14 (number ofteeth: Zal) and a sun gear 16 (number of teeth: Za2). The clutch C1 isadapted to engage or disengage the turbine shaft 40 with or from thestator cylindrical shaft 44. Further, a brake B1 for limitting arotation of the stator cylindrical shaft 44 is provided radially outsideof the clutch C1.

The foregoing brakes B1-B3 and the clutch C1 are so constructed as to beactuated by well-known conventional hydraulic power. A hydraulic unit 60supplying hydraulic pressure to these friction elements is designed tobe switched and controlled at will by a well-known signal processingsystem 62 (micro computer) which outputs a control signal 62a to thehydraulic unit 60 upon receipt for example of a driving condition signalsuch as a speed signal, an acceleration pedal depression signal etc.Function will be described hereunder. In the foregoing planetary geartrain, a speed change of three forward speeds and one reverse speed isperformed by selectively actuating the brakes B1-B3 and the clutch C1 astabulated in the following Table 3.

                  TABLE 3                                                         ______________________________________                                                  Brake & clutch                                                                C1  B1          B2    B3                                            ______________________________________                                        1st         --    --          0   --                                          2nd         --    0           --  --                                          3rd         0     --          --  --                                          Rev         --    --          --  0                                           ______________________________________                                    

In a first speed where only the brake B2 is actuated, the statorcylindrical shaft 44 connected to the sun gear 14 & 16 rotates in adirection opposite to a rotation direction of the turbine shaft 40.Consequently, a reversal torque of the first stator is transmitted as anormal torque from the stator cylindrical shaft 44 through the sun gear16 of the planetary gear assembly 12 to the ring gear 20, and is addedto a normal torque of the turbine 34 to be outputted from the outputgear 26. Namely, the reversal torque is added to the normal torque ofthe turbine 34 in the region where the first stator 36 generates itsreversal torque, so that efficiency and torque ratio are improved.

Namely, as graphically illustrated in FIG. 1a showing a torque ratio tand an efficiency n plotted against a speed ratio e, the efficiency canbe improved from a conventional efficiency characteristic η0 to anefficiency characteristic η1 and the torque ratio can be improved from atorque ratio characteristic t0 to a torque ratio charcteristic t1respectively, in a speed ratio zone smaller than P (speed ratio e=0.55)where the rotation direction of the first stator 36 changes to thenormal direction. In a speed ratio zone larger than or equal to P, thefirst stator 36 runs idle because of the function of the one-way clutch42.

In a second speed where only the brake B1 is actuated, the first stator36 is locked to increase torque transmitted from the turbine 34 in speedratio zone before the first stator 36 runs idle. Further, since thefirst stator runs idle in the speed ratio zone before the second stator38 runs idle, a loss due to fluid of the stator portion can be lessenedso that the efficiency can be improved in this speed ratio zone.

In this second speed zone, the improvements are effected from anefficiency characteristic η0 to an efficiency characteristic η2 and froma torque ratio characteristic t0 to a torque ratio characteristic t2respectively as graphically illustrated by FIG. 1b.

Further, in a third speed where only the clutch C1 is actuated, anefficiency characteristic η3 and a torque ratio characteristic t3 areobtainable.

Finally, in a reverse speed where the brake B3 is actuated, the turbine34 is locked and only the reversal torque is transmitted from the firststator 36 through the sun gear 14 to the planetary gear assembly 10.Thus the output shaft 26 is reversed through the planetary gear 24. Inthis reverse speed, the improvements are effected to provide anefficiency characteristic ηR and a torque ratio characteristic tR asgraphically illustrated by Fig. 1d.

Speed change ratios for each foregoing speed change stage are astabulated in the following Table 4.

                  TABLE 4                                                         ______________________________________                                        Brake & clutch                                                                Turbine                 First stator                                          ______________________________________                                        1st                                                                                    ##STR1##                                                                                          ##STR2##                                         2nd                                                                                    ##STR3##           --                                                3rd     1                   --                                                Rev     --                                                                                                 ##STR4##                                         ______________________________________                                    

On the assumption that the number of teeth: Zal=Za2=33 and Zr2=72 inTable 4; a speed change ratio of the turbine 34 is 2.458 and that of thefirst stator 36 is -2.182 for the first speed, the speed change ratio ofthe turbine 34 is 1.458 for the second speed and 1 for the third speed,and the speed change ratio of the first stator 36 is 3.182 for thereverse speed.

(Effect of the Invention)

As described above, the planetary gear train for the automatictransmission according to the first embodiment of the present inventionincludes the following effect.

In the first speed; the reversal torque of the first stator 36 istransmitted through the stator cylindrical shaft 44 to the sun gear 16of the planetary gear assembly 12. The reversal torque of the firststator 36 thus transmitted is added through the sun gear 14 to thenormal torque of the turbine 34 which is transmitted from the ring gear22 connected to the turbine shaft 40 through the planetary gear 24 tothe planetary carrier 18 so that the efficiency and the torque ratio canbe improved in the region where the first stator 36 rotates in thereverse direction.

Accordingly, as graphically illustrated in FIG. 1a, the efficiency canbe improved from the conventional efficiency characteristic η0 to theefficiency characteristic η1 and the torque ratio can be improved fromthe torque ratio characteristic t0 to the torque ratio characteristic t1respectively, in the speed ratio zone smaller than the point P where therotation direction of the first stator 36 changes to the normaldirection.

In the second speed where only the brake B1 is actuated, the firststator 36 is locked to increase the torque transmitted from the turbine34 in the speed ratio zone before the first stator 36 runs idle.Further, since the first stator runs idle in the speed ratio zone beforethe second stator 38 runs idle, the loss due to fluid of the statorportion can be lessened so that the efficiency can be improved in thisspeed ratio zone.

Consequently, the improvements are effected from the efficiencycharacteristic η0 to the efficiency characteristic η2 and from thetorque ratio characteristic t0 to the torque ratio characteristic t2respectively for obtaining the high torque ratio and high efficiency, asgraphically illustrated by FIG. 1b.

As seen from the above description, the torque ratio and the efficiencycan be improved in the first speed and second speed.

Moreover, the gear train requires only one clutch having complicatedstructure and the long axial length, so that overall sizes of theautomatic transmission can be minimized.

(Second Embodiment)

A second embodiment of the present invention is summarized as follows.In an automatic transmission in which a Ravineaux's planetary gear trainincluding a single row planetary gear and a double row planetary gear,both having one planetary carrier in common, is disposed at a rear stageof a four-element torque converter composed of two stators, a turbineand a pump; a planetary gear train of the automatic transmissionincludes a turbine shaft connecting the turbine to a sun gear of thedouble row planetary gear, a stator cylindrical shaft connecting a firststator with a sun gear of the single row planetary gear, a brake forlimiting the rotation of the stator cylindrical shaft, a brake forlimiting the rotation of the planetary carrier, so that an output istaken out from a ring gear of the single row planetary gear.

The above structure will function as described below.

In a first speed, reversal torque of the first stator is inputted in thesingle row planetary gear and added to the turbine shaft.

In a second speed and fourth speed, the first stator is locked andpermitted to run idle in a speed ratio zone before the second statorruns idle. Thus a high efficiency can be obtained.

In the reverse speed, the turbine is locked to take out the reversaltorque of the first stator.

An automatic transmission providing three forward speeds and one reversespeed for front drive automobile according to the second embodiment willbe described hereunder with reference to FIG. 4. In FIG. 4, a memberwith the same symbol as FIG. 3 or FIG. 1 is a member identical with orcorresponding to that of FIG. 3 or FIG. 1, and only members differenttherefrom will be described hereunder. Further, each friction member isoperated by the hydraulic unit 60 and signal processing system 62 ofFIG. 1 in the same manner and are applied to the following embodimentsin such same.

A so-called Ravineaux's planetary gear train, which will be describedlater in details, is combined with the rear stage of the above-mentionedtorque converter 30 to constitute an automatic transmission.

A sun gear 118 (number of teeth: Za2) is connected to turbine shaft 40,and a planetary carrier 114 is equipped to a rear end portion of turbineshaft 40 through clutch C1. The brake B2 is provided radially outside ofthe planetary carrier 114 and at the rearmost end of the turbine shaft40.

Further, a sun gear 116 (number of teeth: Za1) is connected to thestator cylindrical shaft 44. Brake B1 is connected to an intermediateportion of the stator cylindrical shaft 44. A ring gear 20 (number ofteeth: Zr1) meshing with an outer periphery of a planetary gear 110 isconnected to an output gear 122, and an output is taken out from theoutput gear 122.

Function of the automatic transmission illustrated in FIG. 4 will bedescribed hereunder. In the foregoing planetary gear train, a speedchange of three forward speeds and one reverse speed is performed byselectively actuating the brakes B1-B3 and the clutch C1 as tabulated inTable 5 in details.

In a first speed where only the brake B2 is actuated; a reversal torqueof the first stator 36 is transmitted through the stator cylindricalshaft 44 to the sun gear 116, and is added through a planetary gear 110to a normal torque of the turbine 34 which is transmitted from theturbine shaft 40 to a sun gear 118 and a planetary gear 112. Theefficiency and the torque ratio are improved in the region where thefirst stator rotates in the reverse direction.

Namely, as graphically illustrated in FIG. 1a showing a torque ratio tand an efficiency η plotted against a speed ratio e, the efficiency canbe improved from a conventional efficiency characteristic η to anefficiency characteristic η1 and the torque ratio can be improved from atorque ratio characteristic t0 to a torque ratio characteristic t1respectively, in a speed ratio zone smaller than P where the rotationdirection of the first stator 36 changes to the normal direction. In aspeed ratio zone larger than or equal to P, the first stator 36 runsidle owing to a function of the one-way clutch 42.

In a second speed where only the brake B1 is actuated, the first stator36 is locked to increase torque transmitted from the turbine 34 in aspeed ratio zone before the first stator 36 runs idle. Further, sincethe first stator runs idle in the speed ratio zone before the secondstator 38 runs idle, a loss due to fluid of the stator portion can belessened so that the efficiency can be improved in this speed ratiozone.

In this second speed zone, the improvements are effected from anefficiency characteristic η0 to an efficiency characteristic η2 and froma torque ratio characteristic t0 to a torque ratio characteristic t2respectively as graphically illustrated by FIG. 1b.

Further, in a third speed where only the clutch C1 is actuated, anefficiency characteristic η3 and a torque ratio characteristic t3 areobtainable.

Finally, in a reverse speed where the brake B3 is actuated, the turbine34 is locked, and only the reversal torque is transmitted from the firststator 36 through the sun gear 116 to the planetary gear 10, thus thering gear 120 and the output gear 122 are reversed. In this reversespeed, the improvements are effected to provide an efficiencycharacteristic ηR and a torque ratio characteristic tR as graphicallyillustrated by FIG. 1d.

(Third Embodiment)

In FIG. 5 showing the third embodiment of the present invention, thebrake B3 (FIG. 4) is eliminated and a clutch C2 is connected to theplanetary carrier 114. The brakes and clutches are actuated as tabulatedin Table 5, described later, to perform a speed change of three forwardspeeds and one reverse speed.

(Fourth Embodiment)

In FIG. 6 showing the fourth embodiment for a speed change of fourforward speeds and one reverse speed, the clutch C1 is interposedbetween the sun gear 118 and the turbine shaft 40. These brakes andclutches are actuated as tabulated in the following Table 5 to performthe speed change of four forward speeds and one reverse speed.

A torque ratio characteristic t and an efficiency eeeeacteristic ηbecome the same as in FIG. 1b.

(Fifth Embodiment)

In FIG. 7 showing the fifth embodiment of the present invention; thebrake B3 is eliminated, the clutch C1 is interposed between the sun gear118 and the turbine shaft 40, and a clutch C3 is attached to theplanetary carrier 114. These brakes and clutches are actuated astabulated in the following Table 5 to perform the speed change of fourforward speeds and one reverse speed.

                  TABLE 5                                                         ______________________________________                                               Brake & clutch                                                         Shift    FIG. 4  FIG. 5    FIG. 6                                                                              FIG. 7                                       ______________________________________                                        1st      B2      B2, C2    B2, C1                                                                              B2, C1, C3                                   2nd      B1      B1        B1, C1                                                                              B1, C1                                       3rd      C1      C1, C2    C1, C2                                                                              C1, C2, C3                                   4th      /       /         B1, C2                                                                              B1, C2, C3                                   Rev      B3      B2, C1    B3, C1                                                                              B2, C1, C2                                   ______________________________________                                    

When the brakes and clutches are actuated as tabulated by Table 5, speedchange ratios of the turbine 34 and the first stator 36 can becalculated by equations as tabulated in Table 6. In this instance, ifnumbers of teeth of the sun gears 116, & 118 and the ring gear 120 areassumed as follows,

    Za1=34, Za2=29, Zr1=74                                     (1)

the speed change ratio of the turbine 34 is 2.552 and that of the firststator 36 is -2.176 for the first speed; the speed change ratio of theturbine 34 is 1.489 for the second speed, 1 for the third speed and0.685 for the fourth speed; and the speed change ratio of the firststator 36 is 3.047 for the reverse speed.

                  TABLE 6                                                         ______________________________________                                                Speed change ratio                                                            Turbine    First stator                                               ______________________________________                                        1st                                                                                      ##STR5##                                                                                   ##STR6##                                              2nd                                                                                      ##STR7##    --                                                     3rd       1            --                                                     4th                                                                                      ##STR8##    --                                                     Rev       --                                                                                          ##STR9##                                              ______________________________________                                    

(Effect of the Invention)

As described above, the planetary gear train for automatic transmissionaccording to the second -fifth embodiments of the present inventionprovide the following effect.

In the first speed; the reverse torque of the first stator 36 istransmitted through the stator cylindrical shaft 44 to the sun gear 116,and is added through the planetary gear 110 to the normal torque of theturbine 34 which is transmitted from the turbine shaft 40 to the sungear 118 and the planetary gear 112. The efficiency and torque ratio areimproved in the region where the first stator rotates in the reversedirection.

Accordingly, as graphically illustrated in FIG. 1a, the efficiency isimproved from the conventional efficiency characteristic η0 to theefficiency characteristic η1 and the torque ratio is improved from thetorque ratio characteristic t0 to the torque ratio characteristic t1respectively in the speed ratio zone smaller than P where the rotationdirection of the first stator 36 changes to the normal direction.

In the second speed where only the brake B1 is actuated; the firststator 36 is locked to increase torque transmitted from the turbine 34in the speed ratio zone before the first stator 36 runs idle. Further,since the first stator 36 runs idle in the speed ratio zone before thesecond stator 38 runs idle, the loss due to the stator portion islessened so that the efficiency can be improved in this speed ratiozone.

As graphically illustrated by FIG. 1b, the improvements are effectedfrom the efficiency characteristic η0 to the efficiency characteristicη2 and from the torque ratio characteristic t0 to the torque ratiocharacteristic t2 respectively, so that the high torque ratio and highefficiency can be obtained. The embodiments of FIG. 6 and FIG. 7 canproduce the effect shown by FIG. 1b in the fourth speed.

Since the torque ratios and efficiencies in the first, second and fourthspeeds are improved as described above, the automatic transmissionaccording to the present invention is able to provide the sameperformance as the conventional four forward speeds through means of theforegoing three forward speeds, and the same performance as theconventional five forward speeds through means of the foregoing fourforward speeds. Consequently, as compared with the conventionalautomatic transmission, the same result as adding one stage to the stagenumber of speed change can be obtained by only adding one guide vane tothe torque converter and connecting it to the sun gear, so that thestructure and control are simplified.

Moreover, in the case of FIG. 2, the automatic transmission requiresonly one clutch having the complicated and axially long structure, sothat the overall sizes of automatic transmission is minimized.

(Sixth Embodiment)

A sixth embodiment of the present invention is summarized as follows. Inan automatic transmission in which a Ravineaux's planetary gear trainincluding a single row planetary gear and a double row planetary gearboth having one planetary carrier in common, is disposed at a rear stageof a four-element torque converter composed of two stators, a turbineand a pump; a planetary gear train of the automatic transmissionincludes a turbine shaft connecting the turbine to a sun gear of thesingle row planetary gear, a stator cylindrical shaft connecting a firststator to a sun gear of the double row planetary gear, a brake forlimiting a rotation of the stator cylindrical shaft, a clutch installedbetween said stator cylindrical shaft and the turbine shaft or betweenthe sun gear of the single row planetary gear and the turbine shaft, abrake for limiting a rotation of the ring gear of the single rowplanetary gear, so that an output is taken out from an output gearconnected to the planetary carrier.

The above structure will function as described below.

In a first speed, the reverse torque of the first stator is inputted inthe double row planetary gear to the turbine output torque.

In a second speed and fourth speed, the first stator is locked andpermitted to run idle in a speed ratio zone before a second stator runsidle. Thus, high efficiency is obtained.

In a reverse speed, the turbine is locked to take out the reversaltorque of the first stator.

An automatic transmission providing three forward speeds and one reversespeed for front drive automobile according to a sixth embodiment will bedescribed hereunder with reference to FIG. 8.

A so-called Ravineaux's planetary gear train, which will be describedlater in details, is combined with the rear stage of the above-mentionedtorque converter 30 to constitute an automatic transmission.

A sun gear 216 (number of teeth: Za2) is connected to turbine shaft 40,and the brake B3 is connected to a rear end portion of the turbine shaft40. The brake B2 is equipped to a ring gear 220 (number of teeth: Zr2)meshing with a planetary gear 210.

Further, a sun gear 218 (number of teeth: Za1) is connected to thestator cylindrical shaft 44, and the brake B1 is equipped to anintermediate portion of the stator cylindrical shaft 44. A clutch C1 isinterposed between the stator cylindrical shaft 44 and the turbine shaft40.

A planetary carrier 214 is connected to an output gear 222 from which anoutput is taken out.

The function of the automatic transmission illustrated in FIG. 8 will bedescribed hereunder. In the foregoing planetary gear train, a speedchange of three forward speeds and one reverse speed is performed byselectively actuating (locking) the brakes B1-B3 and the clutch C1 astabulated in Table 8 described later in details.

In a first speed where only the brake B2 is actuated; reverse torque ofthe first stator 36 is transmitted through the stator cylindrical shaft44 to a sun gear 218, and is added through a planetary gear 212 to anormal torque of the turbine 34 which is transmitted from the turbineshaft 40 to a sun gear 216 through a planetary gear 210. The efficiencyand the torque ratio are improved in a region where the first stator 36rotates in the reverse direction.

Namely, as graphically illustrated in FIG. 1a showing a torque ratio tand an efficiency η plotted against a speed ratio e, efficiency isimproved from a conventional efficiency characteristic η0 to anefficiency characteristic η1 and the torque ratio is improved from atorque ratio characteristic t0 to a torque ratio characteristic t1respectively, in a speed ratio zone smaller than P when the rotationdirection of the first stator 36 changes to the normal direction. In aspeed ratio zone larger than or equal to P, the first stator 36 runsidle owing to a function of the one-way clutch 42.

In a second speed where only the brake B1 is actuated, the first stator36 is locked to increase a torque transmitted from the turbine 34 in aspeed ratio zone before the first stator 36 runs idle. Further, sincethe first stator runs idle in the speed ratio zone before the secondstator 38 runs idle, a loss due to fluid of the stator portion islessened so that the efficiency is improved in this speed ratio zone.

In this second speed zone, the improvements are effected from anefficiency characteristic η0 to an efficiency characteristic η2 and froma torque ratio characteristic t0 to a torque ratio characteristic t2respectively as graphically illustrated by FIG. 1b.

Further, in a third speed where only the clutch C1 is actuated, anefficiency characteristic η3 and a torque ratio characteristic t3 areobtainable.

Finally, in a reverse speed where the brake B3 is actuated, the turbine34 is locked, and only the reversal torque is transmitted as a reactiontorque from the first stator 36 through the sun gear 218 and the fixedsun gear 216 to the planetary gear 210 and the planetary gear 212,reversing the ring gear 220 and the output gear 222. In this reversespeed, the improvements are effected to provide an efficiencycharacteristic ηR and a torque ratio characteristic tR as graphicallyillustrated by FIG. 1d.

The conventional Ravineaux's planetary gear train including the singlerow planetary gear and the double row planetary gear both having oneplanetary carrier in common, is constructed as illustrated in FIG. 9.

Namely, 210 is a planetary gear comparatively long in its axialdirection, and meshes with a sun gear 216 to constitute the single rowplanetary gear. Further, the planetary gear 210 is carried by aplanetary carrier 214, a planetary gear 212 meshing with the planetarygear 210 is carried by the planetary carrier 214, and the planetary gear212 meshes with a sun gear 218 to constitute the double row planetarygear. Moreover, the planetary carrier 214 is connected to the outputgear 222.

Brakes B1, B2 & B3 and clutches C1 & C2 for controlling these gears areequipped and actuated as tabulated in the following Table 7 to perform aspeed change of four forward speeds and one reverse speed.

Incidentally, the brake B3 is eliminated for the three forward speeds.

                  TABLE 7                                                         ______________________________________                                        (Prior art)                                                                   Brake & clutch                                                                B1             B2    B3         C1  C2                                        ______________________________________                                        1st     O          --    --       O   --                                      2nd     O          --    --       --  O                                       3rd     --         --    --       O   O                                       4th     --         --    O        --  O                                       Rev     --         O     --       O   --                                      ______________________________________                                         The stage number of speed change has recently been multiplied from three     forward speeds to four forward speeds and further to five forward speeds     in order to improve the performance of tractive force.

In the foregoing conventional planetary gear train, however, the numberof clutches increases with an increase in the stage number of speedchanges to cause a complex structure and troublesome controls.

If a stall torque ratio is increased in order to solve the above problemin the ordinary three-element one-stage torque converter, the followingtroubles will arise.

(1) Because of a decrease in a capacity of torque converter, the size oftorque converter must be enlarged.

(2) The efficiency of torque converter becomes worse in the vicinity ofits coupling point.

(3) A practical application limit of the stall torque ratio is about 3.

These troubles are overcome by the sixth embodiment as described above.

(Seventh Embodiment)

In FIG. 10 showing the seventh embodiment of the present invention, theclutch C1 is interposed between a sun gear 216 and the turbine shaft 40,and the clutch C2 is interposed between a ring gear 220 and the turbineshaft 40. These brakes and clutches are actuated as tabulated in Table 8to perform a speed change of four forward speeds and one reverse speed.

                  TABLE 8                                                         ______________________________________                                        Friction element Speed change ratio                                           FIG. 8    FIG. 10    Turbine    First stator                                  ______________________________________                                        1st   B2      B2, Cl                                                                                    ##STR10##                                                                              ##STR11##                                  2nd   B1      B1, C1                                                                                    ##STR12##                                                                             --                                          3rd   C1      C1, C2     1        --                                          4th   /       B1, C2                                                                                    ##STR13##                                                                             --                                          Rev   B3      B3, C1     --                                                                                      ##STR14##                                  ______________________________________                                    

When the brakes and clutches are actuated as tabulated by Table 8, speedchange ratios of the turbine 34 and the first stator 36 can becalculated by equations as tabulated in Table 8. In this instance, ifnumbers of teeth of the sun gears 216 & 218 and the ring gear 220 areassumed as follows,

    Za1=21, Za2=72, Zr1=36                                     (1)

the speed change ratio of the turbine 34 is 3.000 and that of the firststator 36 is -2.429 for the first speed; the speed change ratio of theturbine 34 is 1.583 for the second speed, 1 for the third speed and0.708 for the fourth speed; and the speed change ratio of the firststator 36 is 2.714 for the reverse speed.

(Effect of the Invention)

As described above, the planetary gear trains for automatic transmissionaccording to the sixth and seventh embodiments of the present inventionprovide the following effect.

In the first speed; the reversal torque of the first stator 36 istransmitted through the stator cylindrical shaft 44 to the sun gear 218,and is added through the planetary gear 212 to the normal torque of theturbine 34 which is transmitted from the turbine shaft 40 to the sungear 216 through the planetary gear 210, so that the efficiency and thetorque ratio is improved in the region where the first stator rotates inthe reverse direction.

Accordingly, as graphically illustrated in FIG. 1a, the efficiency isimproved from the conventional efficiency characteristic η to theefficiency characteristic η1 and the torque ratio is improved from thetorque ratio characteristic t0 to the torque ratio characteristic t1respectively in the speed ratio zone smaller than P where the rotationdirection of the first stator 36 changes to the normal direction.

In the second speed where only the brake B1 is actuated; the firststator 36 is locked to increase the torque transmitted from the turbine34 in the speed ratio zone before the first stator 36 runs idle.Further, since the first stator 36 runs idle in the speed ratio zonebefore the second stator 38 runs idle, the loss due to fluid in statorportion is lessened so that the efficiency is improved in this speedratio zone. Because the embodiment of FIG. 2 produces the effect shownby FIG. 1b in the fourth speed, the automatic transmission according tothe present invention provides the same performance as the conventionalfour forward speeds through means of the foregoing three forward speeds,and the same performance as the conventional five forward speeds throughmeans of the foregoing four forward speeds. Consequently, as comparedwith the conventional automatic transmission, the same result as addingone stage to the stage number of speed change is obtained by only addingone guide vane to the torque converter and connecting it to the sungear, and the structure and control are simplified.

As mentioned above, the torque ratio and the efficiency are improved inthe first, second and fourth speeds.

Moreover, in the case of FIG. 1, the automatic transmission requiresonly one clutch having the complicated and axially long structure, sothat the overall sizes of automatic transmission is minimized.

(Eighth Embodiment)

An eighth embodiment of the present invention is summarized as follows.In an automatic transmission in which a planetary gear train having apair of planetary gear assemblies comprising planetary gears, sun gearsand ring gears, the sun gears being carried rotatably and independently,one planetary carrier of one planetary gear assembly being connected tothe ring gear of the other planetary gear assembly, and an output beingtaken out from the planetary carrier, is disposed at a rear stage of afour-element torque converter composed of two stators, a turbine and apump; a planetary gear train of the automatic transmission includes aturbine shaft connecting the turbine to the sun gear of one planetarygear assembly, a brake for limiting rotation of the turbine shaft, astator cylindrical shaft connecting a first stator to the other sungear, a brake for limitting a rotation of the stator cylindrical shaft,a clutch interposed between the stator cylindrical shaft and the turbineshaft for engaging or disengaging the both shafts, and a brake forlimiting rotation of the other planetary carrier.

The above structure will function as described below.

In a first speed; the planetary carrier not connected to an output sideis locked by the brake, a normal torque of the turbine is combined withthe reverse torque of the first stator at the planetary gear assemblies,and a high torque ratio and a high efficiency are obtained.

In a second speed; the first stator is locked by the brake and permittedto run idle in a speed ratio zone before the second stator runs idle, sothat a high torque ratio and a high efficiency are obtained.

The automatic transmission providing three forward speeds and onereverse speed for front drive automobile according to the eighthembodiment will be described hereunder with reference to FIG. 11.

A planetary gear train which will be described later in details, iscombined with the rear stage of the above-mentioned torque converter 30to constitute the automatic torque converter.

The turbine shaft 40 extends to a right side in FIG. 11 of a planetarygear assembly 310 to be connected to a sun gear 314 (number of teeth:Za2) of the planetary gear assembly 310. The sun gear 314 meshes with aplanetary gear 324 carried by a planetary carrier 318. An output gear326 is connected to a right end of the planetary carrier 318, and a ring325 (number of teeth: Zr1) is fixed to a left end in FIG. 11 of theplanetary carrier 318. The brake B3 for limiting the rotation of theturbine shaft 40 is disposed at a radial outside of the turbine shaft40.

A planetary gear 328 of a planetary gear assembly 312 is carried by aplanetary carrier 329, the planetary carrier 329 is connected to a ringgear 320 (number of teeth: Zr2) of the planetary gear assembly 312, andthe brake B2 is disposed at a radially outside of the planetary carrier329. A clutch C1 is interposed between the turbine shaft 40 and thestator cylindrical shaft 44 connecting to a sun gear 316 (number ofteeth: Za1) of the planetary gear assembly 312, and the clutch C1engages or disengages the turbine shaft 40 with or from the statorcylindrical shaft 44. Further, the brake B1 for limitting the rotationof the stator cylindrical shaft 44 is disposed at a radial outside ofthe clutch C1.

The function is described hereunder. In the foregoing planetary geartrain, a speed change of three forward speeds and one reverse speed isperformed by selectively actuating the brakes B1-B3 and the clutch C1 astabulated in Table 9 described later in details.

In the first speed where only the brake B2 is actuated; a reversaltorque of the first stator 36 is transmitted through the statorcylindrical shaft 44 to the sun gear 316 of the planetary gear assembly312 and outputted as a normal torque from the ring gear 325 integralwith an output shaft. The reverse torque of the first stator 36 is addedthrough the sun gear 314 to a normal torque of the turbine 34 which istransmitted from the turbine shaft 40 through the ring gear 320 of theplanetary gear assembly 310 to the planetary carrier 318 integral withthe output shaft and outputted therefrom. The efficiency and the torqueratio is improved.

As graphically illustrated in FIG. 1a showing a torque ratio t and anefficiency η plotted against a speed ratio e, the efficiency is improvedfrom a conventional efficiency characteristic η0 to an efficiencycharacteristic η1 and the torque ratio is improved from a torque ratiocharacteristic t0 to a torque ratio characteristic t1 respectively, in aspeed ration zone smaller than P where the rotation direction of thefirst stator 36 changes to the normal direction. In a speed ratio zonelarger than or equal to P, the first stator 36 runs idle owing to afunction of the one-way clutch 42.

In the second speed where only the brake B1 is actuated, the firststator 36 is locked to increase the torque transmitted from the turbine34 in a speed ratio zone before the first stator 36 runs idle, thusproviding a high torque ratio, and a high efficiency. In this secondspeed zone, the improvements are effected from an efficiencycharacteristic η0 to an efficiency characteristic η2 and from a torqueratio characteristic t0 to a torque ratio characteristic t2 respectivelyas graphically illustrated by FIG. 1b.

Further, in the third speed where only the clutch C1 is actuated, anefficiency characteristic η3 and a torque ratio characteristic t3 areobtainable.

Finally, in the reverse speed where the brake B3 is actuated, theturbine 34 is locked, and only the reverse torque is transmitted fromthe first stator 36 through the sun gear 316 to the planetary gearassembly 312. Thus the ring gear 320 and the output gear 326 arereversed. In this reverse speed, the improvements are effected toprovide an efficiency characteristic ηR and a torque ratiocharacteristic tR as graphically illustrated by FIG. 1d.

Speed change ratios at each speed change stage mentioned above become astabulated in Table 10 which will be described later in details.

A conventional automatic transmission composed of a planetary gear trainincluding a pair of simple planetary gear assemblies having planetarycarriers and ring gears in common with each other, a friction engagementsystem and a three-element one-stage torque converter, is constructed asillustrated in FIG. 12.

The pair of planetary gear assemblies 310 and 312, composed of planetarygears, planetary carriers and sun gears, are disposed at a rear stage ofa three-element torque converter comprising one stator, a turbine and apump; two sun gears 314 & 316 carried rotatably and independently; aplanetary carrier 318 connected to ring gear 320; and an output can betaken out from the planetary carrier 318.

Brakes B1 & B2 and clutches C1, C2 & C3 for controlling these gears areequipped therein, and actuated as tabulated "0" in the following Table11 to perform a speed change of four forward speeds and one reversespeed.

                  TABLE 11                                                        ______________________________________                                        (Prior art)                                                                   Brake & clutch                                                                B1             B2    C1        C2  C3                                         ______________________________________                                        1st     --         0     --      --  0                                        2nd     0          --    --      --  0                                        3rd     --         --    --      0   0                                        4th     0          --    --      0   --                                       Rev     --         0     0       --  --                                       ______________________________________                                    

In the foregoing conventional planetary gear train, however, a largenumber of clutches are necessary and result in complex structure andtroublesome control.

These problems are eliminated by the eighth embodiment as describedabove.

(Ninth Embodiment)

An automatic transmission providing four forward speeds and one reversespeed for front drive automobile according to the present invention willbe described hereunder with reference to FIG. 13.

In FIG. 13, the clutch C2 is interposed between the sun gear 314 and theturbine shaft 40, and the clutch C1 is interposed between the planetarycarrier 329 and the turbine shaft 40.

In the above-mentioned planetary gear train, the brakes and clutches areactuated as tabulated in the following Table 9 to perform a speed changeof four forward speeds and one reverse speed.

                  TABLE 9                                                         ______________________________________                                                     brake & clutch                                                                FIG. 1                                                                              FIG. 13                                                    ______________________________________                                        1st            B1      B2, C2                                                 2nd            B1      B1, C2                                                 3rd            C1      C1, C2                                                 4th            /       B1, C1                                                 Rev            B3      B3, C2                                                 ______________________________________                                    

When the brakes and clutches are actuated as tabulated by Table 9, speedchange ratios of the turbine 34 and the first stator 36 will become astabulated by the following Table 10.

                                      TABLE 10                                    __________________________________________________________________________    Speed change ratio                                                            Turbine               First stator                                            __________________________________________________________________________    1st                                                                                 ##STR15##                                                                                      ##STR16##                                              2nd                                                                                 ##STR17##       --                                                      3rd  1                --                                                      4th                                                                                 ##STR18##       --                                                      Rev  --                                                                                              ##STR19##                                              __________________________________________________________________________

In Table 10, if numbers of teeth are assumed as Za1=36, Za2=42 andZr1=Zr2=75; the speed change ratio of the turbine 34 is 2.786 and thatof the first stator 36 is -2.083 for the first speed; the speed changeratio of the turbine 34 is 1.579 for the second speed, 1 for the thirdspeed and 0.676 for the fourth speed; and the speed change ratio of thefirst stator 36 is 2.726 for the reverse speed.

(Effect of the Invention)

As described above, the planetary gear trains for automatic transmissionaccording to the eighth and ninth embodiments of the present inventionprovide the following effect.

In the first speed; a reverse torque of the first stator 36 istransmitted through the stator cylindrical shaft 44 to the sun gear 316of the planetary gear assembly 312 and outputted as a normal torque fromthe ring gear 325 integral with an output shaft, and the reversal torqueof the first stator 36 is added through the sun gear 314 to a normaltorque of the turbine 34 which is transmitted from the turbine shaft 40through the ring gear 320 of the planetary gear assembly 310 to theplanetary carrier 318 integral with the output shaft and outputtedtherefrom. The efficiency and the torque ratio are improved.

Accordingly, as graphically illustrated in FIG. 1a, the efficiency isimproved from a conventional efficiency characteristic η0 to anefficiency characteristic η1 and the torque ratio is improved from atorque ratio characteristic t0 to a torque ratio characteristic t1respectively, in the speed ratio zone smaller than P where the rotationdirection of the first stator 36 changes to the normal direction.

In a second speed where only the brake B1 is actuated, the first stator36 is locked to increase torque transmitted from the turbine 34 in aspeed ratio zone before the first stator 36 runs idle, and theimprovements are effected from an efficiency characteristic η0 to anefficiency characteristic η2 and from a torque ratio characteristic t0to a torque ratio charcteristic t2 respectively as graphicallyillustrated by FIG. 1b. Thus, a high torque ratio and a high efficiencycan be improved.

As mentioned above, the torque ratio and the efficiency are improved inthe first and second speeds.

Moreover, the automatic transmission requires only one clutch having thecomplicated and axially long structure, so that the overall sizes ofautomatic transmission is minimized.

What is claimed is:
 1. In an automatic transmission incorporating aplanetary gear transmission at a rear stage of a four-element torqueconverter comprising two stators, a turbine and a pump; a planetary geartrain for an automatic transmission, wherein reverse torque of a firststator running in a reverse direction relative to a forward runningdirection of the turbine in a first low speed ratio zone is convertedinto torque in said forward running of said torque converter directionby said planetary gear train, so that a torque output from said firststator running in said first direction is added to an output shaft ofsaid transmission when said planetary gear transmission is in said firstlow speed ratio zone; a friction element for limiting rotation of saidfirst stator in said first speed ratio zone where said first statorrotates in said reverse direction said first stator having a one-wayclutch for transmitting torque in said reverse direction and for runningidle, when said first stator rotates in a forward running direction sothat fluid loss in the stator portion of said torque converter isminimized when a second speed of said planetary gear transmission isselected.
 2. In an automatic transmission, in which a Simpson'splanetary gear train having a pair of planetary gear assemblies eachcomprising a planetary gear, a sun gear and a ring gear, the sun gear ofone planetary gear assembly being connected to the sun gear of the otherplanetary gear assembly, a planetary gear carrier connected to theplanetary gear of one of said planetary gear assemblies and connected tothe ring gear of the other of said planetary gear assesmblies, and anoutput being taken out from said planetary carrier, is disposed at arear stage of a four-element torque converter composed of two stators, aturbine and a pump; the planetary gear train of said automatictransmission including a turbine shaft connecting the turbine of saidtorque converter to the ring gear of one of said planetary gearassemblies, a brake for limiting the rotation of said turbine shaft, astator cylindrical shaft connecting a first stator of said torqueconverter to the sun gears of said Simpson's planetary gear train, abrake for limiting a rotation of said stator cylindrical shaft, and aclutch interposed between said stator cylindrical shaft and said turbineshaft for engaging and disengaging said turbine shaft and said statorshaft, respectively.
 3. A planetary gear train of an automatictransmission as set forth in claim 2, in which said first stator isconnected to said stator cylindrical shaft through a oneway clutch whichconnects said first stator to said stator shaft in a low speed ratiozone where said first stator rotates in a direction reverse to a forwarddirection of rotation of said turbine and disconnects said first statorfrom said stator shaft and leaves said first stator to run idle in ahigh speed ratio zone where said first stator rotates in the forwarddirection with said turbine.
 4. A planetary gear train of an automatictransmission as set forth in claim 2, in which said brake limits therotation of said stator cylindrical shaft when a first speed isselected.
 5. A planetary gear train of an automatic transmission as setforth in claim 2, in which said clutch limits the rotation of saidstator cylindrical shaft in said low speed ratio zone when a secondspeed is selected.
 6. In an automatic transmission in which a Simpson'splanetary gear train having a pair of planetary gear assembliescomprising planetary gears, sun gears and ring gears, said sun gearsbeing connected to each other, a planetary carrier connected to theplanetary gear of one of said planetary gear assemblies and connected tothe ring of the other gear of said planetary gear assemblies, and anoutput being taken out from said planetary carrier, is disposed at arear stage of a four-element torque converter composed of two stators, aturbine and a pump; the planetary gear train of said automatictransmission including a turbine shaft connecting said turbine to thering gear of one of said pair of planetary gear assemblies, a brake forlimiting rotation of said turbine shaft, a stator cylindrical shaftconnecting a first stator of said two stators to said sun gears, a brakefor limiting the rotation of said stator cylindrical shaft connected tosaid first stator, a clutch interposed between said stator cylindricalshaft connected to said first stator and said turbine shaft for engagingand disengaging said shafts, said first stator being connected to saidstator cylindrical shaft through a one-way clutch which connects saidfirst stator to said stator cylindrical shaft in a low speed ratio zonewhere the first stator rotates in a reverse direction and for runningidle in a high speed ratio zone where said first stator is rotated in aforward direction, said brake limiting the rotation of said statorcylindrical shaft connected to said first stator in a high speed ratiozone when a second speed is selected, said stator cylindrical shaftconnected to said first stator being connected to said sun gears of saidpair of planetary gear assemblies, a planetary carrier carrying aplanetary gear of one of said planetary gear assemblies and meshing withone sun gear equipped with a brake for second speed, a ring gear meshingwith said one sun gear connected to an output planetary carrierconnecting to the other planetary gear, the other ring gear being freelyengaged with or disengaged from said turbine shaft through a brake forthird speed, a friction element for limiting rotation of the turbine toexert reverse torque on said first stator when a reverse speed isselected, and one element of the planetary gear train connected andfixed to the turbine so as to take out the reversal torque of the firststator while decelerating the first stator.
 7. In an automatictransmission having a four-element torque converter composed of a firststator, a second stator, a turbine and a pump and a planetary gear trainat a rear stage of said torque converter, said planetary gear trainhaving a pair of planetary gear assemblies each comprising a planetarygear, a sun gear, a ring gear, and a planetary carrier the planetarycarrier of one of said planetary gear assemblies being connected to thering gear of the other of said planetary gear assemblies, and an outputbeing taken out from said planetary gear carriers, said automatictransmission having a turbine shaft connecting said turbine to the ringof said one of said planetary gear assemblies, a brake for limitingrotation of the turbine shaft, a stator cylindrical shaft connectingsaid first stator to the sun gears of said pair of planetary gearassemblies, a brake for limiting the rotation of said stator cylindricalshaft, a clutch interposed between said stator cylindrical shaft andsaid turbine shaft for engaging or disengaging both said shafts, and abrake for limiting rotation of the planetary carrier of said other ofsaid planetary gear assemblies.
 8. A planetary gear train of anautomatic transmission as set forth in claim 7, in which said firststator is connected to said stator cylindrical shaft through a one-wayclutch which connects said first stator to said stator cylindrical shaftin a low speed ratio zone where said first stator rotates in a reversedirection from said turbine and runs idle in a high speed ratio zonewhere said first stator rotates in a forward direction with saidturbine.
 9. A planetary gear train of an automatic transmission as setforth in claim 7, in which said brake for limiting the rotation of saidcylindrical shaft limits the rotation of said stator cylindrical shaftwhen said automatic transmission is in first speed.
 10. A planetary geartrain of an automatic transmission as set forth in claim 7, in whichsaid clutch between said stator shaft and said turbine shaft limits therotation of said stator cylindrical shaft in a low speed ratio zone whena second speed of said automatic transmission is selected.
 11. In anautomatic transmission having a four-element torque converter composedof a first stator, a second stator, a turbine and a pump and a planetarygear train at a rear stage of said torque converter, said planetary geartrain having a pair of planetary gear assemblies, each of said pair ofplanetary gear assemblies having a planetary gear, a sun gear and a ringgear, one of said planetary gear assemblies having a planetary gearcarrier carrying the ring gear of the other of said planetary gearassemblies, and an output being taken out from said planetary gearcarrier, and an output being taken out from said planetary gear carrier,said automatic transmission having a turbine shaft connecting saidturbine of said torque converter to the ring gear of one of saidplanetary gear assemblies, a brake for third speed for limiting rotationof said turbine shaft, a stator cylindrical shaft connecting said firststator to the sun gear of each of said pair of planetary gear assembliesand connecting said sun gears to each other, a brake for limitingrotation of said stator cylindrical shaft, a clutch interposed betweensaid stator cylindrical shaft and said turbine shaft for engaging anddisengaging said shafts with each other, a brake for second speed forlimiting the rotation of a planetary gear carrier of said other of saidplanetary gear assemblies, said first stator being connected to saidstator cylindrical shaft through a one-way clutch which connects saidfirst stator to said stator shaft in a low speed ratio zone where thefirst stator rotates in a reverse direction relative to said turbine andruns idle in a high speed ratio zone where the first stator rotates inthe same direction as the turbine, said brake for second speed limitingthe rotation of said stator cylindrical shaft when a first speed isselected, and said clutch limiting the rotation of said statorcylindrical shaft in a low speed ratio zone when a second speed iselected.
 12. In an automatic transmission in which a planetary geartrain having a pair of of simple planetary gear assemblies comprisingplanetary gears, sun gears and ring gears, two sun gears being carriedrotatably and independently, a planetary gear carrier of one planetarygear assembly of said planetary gear assemblies being connected to thering gear of the other planetary gear assembly of said planetary gearassemblies, and an output being taken out from the planetary carrier, isdisposed at a rear stage of a four-element torque converter composed oftwo stators, a turbine and a pump; a planetary gear train of theautomatic transmission including a turbine shaft connecting the turbineto the ring gear of one planetary gear assembly, a brake for third speedfor limiting a rotation of the turbine shaft, a stator cylindrical shaftconnecting a first stator to the other sun gear, a brake for limitingrotation of the stator cylindrical shaft, a first clutch interposedbetween said one planetary carrier and the turbine shaft, a brake forsecond speed for limiting rotation of a planetary gear carrier of theother planetary gear assembly of said planetary gear assemblies, asecond clutch interposed between the sun gear meshing with said otherplanetary gear and the turbine shaft, said first stator being connectedto the stator cylindrical shaft through a one-way clutch which connectsthe former to the latter in a low speed ratio zone where the firststator rotates in a reverse direction and runs idle in a high speedratio zone where the first stator is switched to rotate in a normaldirection, said brake working to limit the rotation of the statorcylindrical shaft when a first speed is selected, and said first clutchworking to limit the rotation of the stator cylindrical shaft in a lowspeed ratio zone when a second speed is selected.